1. Field of the Invention
The present invention relates to a hollow golf club head, particularly to a golf club head having a shape of a wood type or a shape approximately the same. More particularly, the invention relates to a golf club head in which at least a central portion of a face portion is made of an amorphous metal.
2. Description of the Related Art
A metal golf club head of a hollow shell structure has come to wide use as a wood-type golf club head, such as a driver or a fairway wood. Generally, a hollow wood-type golf club head has a face portion for hitting a ball; a crown portion forming the upper surface of the golf club head; a sole portion forming the lower surface of the golf club head; a side portion forming side faces on its toe, rear, and heel sides; and a hosel portion. A shaft is inserted into the hosel portion, and fixed thereto by means of an adhesive, or the like. Meanwhile, recently, a number of golf clubs called utility clubs have also been commercially available. A variety of golf clubs having heads analogous to the above-mentioned wood-type golf club head (that is, having a face portion, a sole portion, a side portion, a crown portion, and a hosel portion) are also commercially available as a type of such utility golf clubs.
As a metal for forming the hollow golf club head, an aluminum alloy, stainless steel, or a titanium alloy has been used. Among them, a titanium alloy in particular has been in wide use in recent years.
Generally, when a hollow golf club head is increased in volume, the sweet spot thereof can be expanded. When a volume of a golf club head is increased, accompanying therewith, the weight thereof is likely to be increased. In order to prevent the golf club head from being increased in weight, consideration has been given to employment of a fiber-reinforced plastic whose specific gravity is lower than those of the above-listed metals as the constituent material of the golf club head.
JP-A-2001-340499 discloses a golf club head whose face portion and sole portion are made of a metal, and other portions; that is, a crown portion, and a side portion on the toe and heel sides, are made of a carbon-fiber reinforced thermosetting plastic (CFRP). When the crown portion is made of CFRP, deformation of the crown portion upon hitting a ball is increased, thereby enabling an increase in a launch angle, or a higher coefficient of restitution. However, in the golf club head, a peripheral edge of the face portion is butt-joined to the crown portion and the side portion made of CFRP. When a ball is hit, extreme stress is applied to a joint portion between the crown portion and the face, and that between the side portion and the face. Accordingly, after repeated use, the joints may be separated.
JP-A-2003-62130 discloses a golf club head, wherein a front edge portion of a crown portion, a front edge portion of a sole portion, and front edge portions of two side portions are integrally forged with the face portion, from titanium; a body made of a resin material is affixed to the titanium face element so as to continue therefrom; and an aluminum plate is disposed on the sole portion. The face element includes the front edge portion of the crown portion, the front edge portion of the sole portion, and the front edge portions of the two side portions. Accordingly, a bonding strength between the face element and the resin body can be rendered greater than that of the joint between the crown portion made of a CFRP and the metal face disclosed in JP-A-2001-340499. Meanwhile, in the golf club head disclosed in JP-A-2003-62130, the aluminum plate of the sole portion overlaps the titanium face element from below.